Photographic color correction



Patented May 6, 1952 PHOTOGR-APHIC COLOR CORRECTION Ronald Bernard Collins, Douglas James Fry, and Oliver Edmund Pratt, Ilford, England, assignors to Iliord Limited, Ilford, England, a British Company No Drawing. Application August 31, 1949, Serial 7 Claims. (01. 95.-2)

This invention relates to colour photography and particularly to methods and materials for obtaining corrected colour images.

. Most of the modern processes of colour photography are based on the use of an integral tripack material which comprises a support and, superimposed on one side of the support, three silver halide emulsion layers, one of which is sensitised for the red region of the spectrum, one is sensitised for the green region of the spectrum,and the other is not specially sensitised. Silver halide emulsion layers are normally sensitive to blue, and accordingly it is arranged that the not-specially-sensitised emulsion, which is sensitive to blue, is an outer layer of the threeemulsion layer assembly and there is provided a blue-absorbing layer betweenit and the remaining emulsion layers. Thus, when the material is exposed to a coloured object the blue, green and red records are recorded in their appropriate layers. Variations in the structure of the material are possible: for example the order of the layers may be varied.

For the sake of brevity the not-specially-sensitised emulsion will hereinafter be referred to as the blue-sensitive emulsion since it is in fact the only emu sion which is allowed to record the blue light received from the subject photographed. It will further be understood that in speaking of the blue-sensitive emulsion as an outer layer, it is meant that the blue-sensitive layer is not located between the other two layers: it mav be closest to the support or the most remote from the support, but should in either case be the layer on which the light of the exposure is first incident.

When a material of the type described above contains co our-formers, and is subjected to "colour development, coloured images are formed in situ with the s l er ima es. Colourformers are com ounds which combine with the oxidation products formed during development by means of an aromatic primary amino developing agent, to form awomethine or quinoneimine dyestufi images in situ with the developed silver images, and colour development is the term applied to the production of such dyestuff images.

The colour-formers may be included in the emulsion layers or may be in layers adjacent thereto, or may be contained in co loid media, e. g. grains of hydrophilic colloid, dispersed through the emulsion layers.

By employing colour-formers which yield dyes whlch are complementary to the sensitivity of In Great Britain September 7,

the layers, 1. e. a colour-former yielding a yello dye in the blue-sensitive layer, a colour-former yielding a magenta dye in the green-sensitive layer, and a colour-former yielding a cyan dye in the red-sensitive layer, it is possible, by a reversal technique, to obtain a positive colour transparency in full colour.

In an alternative technique the original material may be processed to a negative and this may be copied on to another multilayer photographic material, which in turn may be developed to a positive: in this negative-positive technique the colour-formers present in the layers of the materials need not be such as will yield dyes complementary in colour to the sensitivities of the emulsions (as is broadly essential in the reversal technique), but providing the dyes are respectively subtractive to the primaries they may be generated in any of the emulsion layers, the correction being efiected by an appropriate choice of colour sensitivity and colour-former assembly in making the positive print. Such processes are referred to as false-colour processes and in further explanation of the technique, attention is drawn to British Patents Nos. 475,784 and 475,786.

Though processes such as those described above could theoretically yield excellent results, dlfficulties arise in practice from several sources. A principal source of dimculty is that it is impossible to find three colour-formers which will yield ideally perfect dye images. There is always some departure from perfection and it is usually that the dye absorbs light of wavelengths which it should, ideally, freely transmit. Cyan dyes are generally the worst, absorbing quite appreciably in the blue and green, while magenta dyes generally absorb too much in the blue. The net result is that the balance of the colours is disturbed and a true colour rendering is not obtained.

The present invention provides processes whereby the effect of the unwanted absorptions may be corrected, and it employs the technique now generally known as masking. In brief this technique amounts to the following: each dye image which absorbs light in wavelengths which it should ideally transmit is provided with a complementary image (1. e. a positive where the original is a negative and vice versa) which absorbs light of said wavelengths to an extent such that the absorption of light of such wavelengths over both images is substantially constant. It will be appreciated that by this means the effect of the unwanted absorptions is masked out in the sense that, over those wavelengths, the layer containing the dye image will cast no image on a printing material.

Many methods have been suggested for achieving this end. The bulk of them rely on the production of separate masks which are bound up in register with the original. Latterly, however, attention has been directed to the production of masks which are formed integrally with the original material. The present invention is directed to an improved process of this type.

In British Patent No. 591,124 there is described a method of forming a coloured colloid layer which comprises forming a layer of a water-permeable colloid containing a surface-active compound and thereafter applying to such layer an aqueous solution of a dyestuff which has an opposite electrostatic charge to that carried by said surface-active compound. The surface-active compound and the dye appear to form a complex which, thoughstable under ordinary conditions, canbe broken down .by suitable treatment. Thus in British Patent No. 591,122 there is described a process in which a layer containing such a dye complex is treated with a substance which forms with the surface-active compound a compound which is more stable than the dye complex, and the layer is then washed with water, thus washing out the freed dyestuff.

In British Patent No. 591,123 multilayer elements for colour photography are described in which one or more layers contain surface-active compounds and processes are described whereby such layers may be coloured by the absorption of a dye by such layers selectively, the colouration being due to the combination of the dye with the surface-active compound, and may be decolourised by a subsequent treatment as described in British Patent No. 591,122.

It has been found that many of the compounds which are now well known for use as substantive colour-formers, l. e. colour-formers which do not diffuse or migrate appreciably in gelatin layers of photographic material, have the property of combining with dyestuffs and may therefore serve to replace the surface-active compounds in the processes of the aforesaid British Patent Nos. 591,122, 591,123 and 591,124. The present invention makes use of this property in effecting the masking of colour photographic images for colour correction.

In accordance with the present invention, in a colour photographic process there is employed in at least one emuslion layer a substantive colourformer which has an acid substituent grouping in the position at which the colour-former couples on colour-development, which grouping is eliminated on such colour-coupling, which colourformer is therefore capable of combining with a basic dye to form a dye complex, a dye image is formed by colour development in said layer and the layer is thereafter treated with a basic dyestuff to form a complex with the residual colourformer, the colour of the complex being different from that of the said colour-formed dye image.

In the preferred form of the invention the colour of the complex is such that it absorbs only light of those wave-lengths for which the colourformed dye image shows an unwanted absorption, so that the absorption of those wavelengths is substantially constant throughout the layer. There is thus formed an image in dye complex complementary (i. e. positive where the colourformed image is negative and. vice versa) to the colour-formed image and serving as a mask for the unwanted absorptions thereof. Colourformed cyan dye images generally absorb too highly in the blue and, to a lesser extent, in the green regions of the spectrum and accordingly the optimum colour for the masking image is an orange. Colour-formed magenta dye images generally absorb too highly in the blue region of the spectrum and a yellow masking image is therefore suitable. Colour-formed yellow images, however, generally require little correction and for that reason it .is preferred, in the present invention, that the yellow colour-former should not have surface-active properties. It will be appreciated therefore that a fair degree of correction can be effected by the provision of yellow images complementary to the cyan and magenta images only, and it is therefore possible to efiect a substantial colour correction by the use of a single masking dye.

The following are examples of colour-formers, as hereinbefore defined, which are available for use in the present invention in association with the use of a basic dye for themasking-image:

i-stearoylamino benzoylacet-3':5'-dicarboxyanilide (yielding a yellow'image) l-methoxy benzoylacet-4-carboxy-6'-N-octadecyl-N-methyl-amino anilide (yielding a yellow image).

1- 3'-sulpho-4-phenoxyphenyll -3-heptadecyl-5- pyrazolone (yielding a magenta image).

l-hydroxy-4- sulpho-2- naphthoyloctadecylamide (yielding a cyan image).

l-hydroxy-2- naphthoyl-2 (N-methyl-N-octadecylamino)5'sulphoanilide (yielding a cyan image).

Suitable basic dyes for-use with-these are:

Auramine 0 (Colour Index No. 655) Rhodamine B (Colour Index No. 749) Rosaniline Hydrochloride (Colour Index No. 677) Malachite Green (Colour Index No. 657) The word "Rhodamine is a registered trademark.

The fundamental procedure of the present invention may be illustrated by considering .a single layer of photographic emulsion coated on a support, for example a layer of a silver iodobromide emulsion having a coating weight of 20 mgm. of silver per squaredecimetre and 5 mgm. per square decimetre of the colour-former 1-hydroxy-2-N- stearylacetamino napthalenei-sulphonic acid. This material was exposed behind a step wedge and colour developed, thus producing a negative cyan dye image. The silver and silver halide in the layer were then removed by treatment with Farmers reducer. The material was then bathed in a 0.1% aqueous solution of Auramine O and the film was washed in running water for 20 minutes. It was found that a yellow positive image was obtained complementary to the negative cyan image. This yellow positive image serves as a. mask for the undesired blue absorption of the cyan dye. By employing a magenta dye instead of the Auramine O a mask could similarly be obtained which would correct for the undesired green absorption of the cyan dye. The masking image thus formed may be removed at any desired time by following the procedure set out in British Patent No. 591,122 referred to above. If the mask were again required it could be reformed in a similar manner in the same or a different dye. The density of the mask can be decreased by water washing or by controlled treatment with a cation-active compound.

Example 1 A photographic element is prepared consisting of the following layers in super position in the order stated:

(a) Transparent colourless film support.

(1)) Gelatino silver iodobromide emulsion sensitised to the red region of the spectrum bymeans of 3.3'diethyl 5:615:6'-tetramethoxy-9- [1"-ethyl-2 -phenyl-5 -methyl-3 -keto pyrazolyl (4) thiacarbocyanine bromide and containing the cyan colour-former 1-hydroxy-4-sulpho-2-naphthoyloctadecylamide.

(c) Gelatino silver iodobromide emulsion sensitised to the green region of the spectrum by means of 3:3:9-triethyl-5:5'-diphenyl oxacarbocyanine iodide and containing the magenta colour-former 1-phenyl-B-heptadecyl-B-pyrazolone-4-sulphonic acid.

(d) Filter layer consisting of a dispersion of yellow colloidal silver in gelatin.

'(e) Gelatino silver iodobromide emulsion having a natural sensitivity in the blue region of the spectrum and substantially insensitive to the green and red regions of the spectrum and containing the yellow colour-former 4.4.-'-dibenzoylacetbenzidide.

The above element is exposed to a multicoloured object and the film is then colour devel oped in a developer of the following composition:

N.N-diethyl p-phenylene diamine hydrochloride g 0.4. Sodium carbonate (NazCOa.10 H) (20% solution cc 160 Sodium sulphate (Na2SO3.7 H20) (20% solution) cc Potassium bromide g 0.1 Water to make cc 400 The element is then bathed in Farmers reducer which removes silver and silver salts leaving a negative colour image of the original object.

The element is then bathed in an aqueous solution containing 0.1% Auramine O and 0.05% Rhodamine B. The film is then washed in water for minutes when a yellowish-red image is obtained in the greenand red-sensitive layers only where no magenta or cyan dye image was produced during the colour development. This yellowish-red image forms a satisfactory masking image for the imperfections of the magenta and cyan colour-formed images so that when the element is used as a medium from which positive colour records are to be made a substantial degree of colour correction is achieved.

Example 2 A photographic element was prepared as in Example 1 except that the colour-formers in layers (c) and (e) were respectively l-m-stearoylamino phenyl-3-methylsulpho-S-pyrazolone and stearoylacet-o-chloranilide.

The element was processed to produce a negative colour record as in Example 1 and was then bathed in a 0.1% solution of Auramine O. After washing in water a yellow masking image is formed complementary to the cyan and magenta colour-formed images.

It will be appreciated that many variations may be made within the scope of the present invention. Thus, for example, the original multilayer photographic element may be processed to a positive transparency so that it may be viewed as such and then at any subsequent time may be treated to form mashing images in the layers in order to correct the undesired absorptions of the colour-formed images, and thus provide a satisfactory medium for the production of duplicate colour prints.

In a modification of this invention the complex between the colour-former and the dye may be formed initially and introduced as such into the photographic layers, or may be formed in situ in the photographic layers at any stage in the handling of the material. If this procedure is adopted, however, care should be taken to avoid the use of any strongly acid or strongly alkaline processing bath as this may affect the complex undesirably.

It will be appreciated that the present invention presents important advantages over processes which have previously been described for the production of integral masking images. Thus, no special colour-formers are required since colour-formers which possess the desired properties are already well-known. The method is applicable both to the treatment of reversal material and to material which is processed first to a negative and from which positive copies are made. The masking dye images can be removed whenever desired and replaced whenever desired, and in being replaced may be changed in hue. Further, the density of the masking image can be quite simply controlled by regulating the concentration of dye in the dye bath used and the time of bathing, and also by washing or the controlled removal of any excess density.

It will further be appreciated that while previous proposals for integral masking have used substances which can be converted into dyes when required, the present invention makes use of the unused colour-former merely as an absorbent for the dye and it is not itself converted to a dye.

What we claim is:

1. A process for the production of a colourcorrected photographic record which comprises subjecting a photographic material which contains in at least one layer; a substantive colourformer which has in the position at which the said colour-former couples on colour development an acid grouping selected from carboxylic and sulphonic acid groups and also contains a record dye image obtained by such coupling development, the said dye image undesirably absorbing to some extent light of wavelengths which it is desired that it should transmit, to treatment with a basic dye, thereby forming with the residual colour-former in the said layer an image of opposite sign to the said record dye image, the said image of opposite sign being in a complex of such residual colour-former and said basic dye, the hue and intensity of such image of opposite sign being such that it absorbs light of at least some of the wavelengths which the record dye image undesirably absorbs, so that the absorption of such wavelengths is substantially uniform over the whole layer, and transmits more freely than the record dye image in the remaining wavelengths.

2. A process for the production of a colourcorrected photographic record which comprises exposing to a coloured object a multi-layer photographic material comprising a support and superimposed on one side of the support three silver halide emulsion layers one of which is sensitised for the red region of the spectrum, one is sensitised for the green region of the spectrum, and one is sensitive only to the blue region of the spectrum, the said material containing substantive colour-formers respectively in coactive relationship to said emulsion layers and adapted severally to yield, on colour-development, dye images which are subtractive with respect to the primary colours, at least one of said colourformers (A) having in the position at which it couples on colour-development an acid grouping selected from carboxylic and sulphonic acid groups and yielding on colour-development a record dye image which undesirably absorbs to some extent light of wavelengths which it is desired that it should transmit, subjecting the said photographic material to colour-development to form dye record images in the three subtractive colours, and treating the resulting material with abasic dyestuff, thereby forming with the residual colour-former (A) an image of opposite sign to the record dye image from the colourformer (A) in a complex of such residual colourformer and said basic dye, the hue and intensity of such image of opposite sign being such that it absorbs light of at least some of the wavelengths which the record dye image in the layer containing colour-former (A) undesirably absorbs, so that the absorption of such wavelengths is substantially uniform over the whole of said layer, and transmits more freely than the said record dye image in the remaining Wavelengths.

3. A process for the production of a colourcorrected photographic record which comprises exposing to a coloured object a multi-layer photographic material comprising a support and superimposed on one side of the support three silver halide emulsion layers one of which is sensitised for the red region of the spectrum, one

"is sensitised for the green region of the spectrum, and one is sensitive only to the blue region of the spectrtm, the said material containing substantive colour-formers respectively in coactive relationship to said emulsion layers and adapted severally to yield, on colour-development, dye images which are yellow, magenta and cyan in colour, the yellow colour-former being free from acid groups and one of the magenta and cyan colour-formers having in the position at which it couples on colour-development an acid grouping selected from carboxylic and sulphonic acid groups and yielding on colour-development a record dye image which undesirably absorbs to 8 in each of the layers containing such colourformers.

5. A process according to claim 3 wherein both the magenta and cyan colour-formers are acid colour-formers and images of sign opposite to the record images are formed in a complex of the residue of such colour-formers and a yellow to red basic dye in each of the layers containing such colour-formers.

6. A process for the production, of a colourcorrected photographic record which comprises exposing to a coloured object a multi-layer photographic material comprising a support and superimposed on one side of the support three silver halide emulsion layers one of which is sensitised for the red region of the spectrum, one is sensitised for the green region of the spectrum, and one is sensitive only to the blue region of the spectrum, the said material containing substantive colour-formers respectively in coactive relationship to said emulsion layers and adapted severally to yield, on colour-development, dye images which are yellow, magenta and cyan in colour, the yellow colour-former being free from acid groups and one of the magenta and cyan colour-formers having in the position at which it couples on colour-development an acid grouping selected from carboxylic and sulphonic acid groups and yielding on colour-development a record dye image which absorbs undesirably to some extent light of wavelengths which it is desired that it should transmit, subjecting the said photographic material to colour-development to form dye record images in yellow, magenta and cyan and treating the resultin material with a basic dyestuff, thereby forming with the residual acid colour-former an image of opposite sign to the record dye image from' such acid colourformer in a complex of residual acid colourformer and said basic dye, the hue and intensity of such image of opposite sign being such that it absorbs light of at least some of the wavelengths which the record dye image in the said layer containing the said acid colour-former undesirably absorbs, so that the absorption of such wavelengths is substantially uniform over the some extent light of wavelengths which it is desired that it should transmit, subjecting the said photographic material to colour-development to form dye record images in yellow, magenta and cyan and treating the resulting material with a basic dyestufi, thereby forming with the residual acid colour-former an image of opposite sign to the record dye image from such acid colour-former in a complex of residual acid colour-former and said basic dye, the hue and intensity of such image of opposite sign being such that it absorbs substantially uniformly li-ht of at least some of the wavelengths which the record dye image in the said layer containing the said acid colour-former undesirably absorbs, so

that the absorption of such wavelengths is substantially uniform over the whole of said layer,

and transmits more freely than the said record whole of said layer, and transmits more freely than the said record dye image in the remaining wavelengths, makin a copy in colour of the complete photographic record thus obtained by printing said record on to multilayer colour photographic material and thereafter removing the basic dye from the photographic record by treating the said record with a colourless cation-active compound.

7. A process for the production of a colourcorrected photographic record which comprises exposing to a coloured object a multilayer photographic material comprising a support and superimposed on one side of the support three silver halide emulsion layers one of which is sensitised for the red region of the spectrum, one is sensitised for the green region of the spectrum, and one is sensitive only to the blue region of the spectrum, the said material containing substantive colour-formers respectively in coactive relationship to said emulsion layers and adapted severally to yield, on colour-development, dye images which are yellow, magenta and cyan in colour, the yellow colour-former being free from acid groups and one of the magenta and cyan colour-formers having in the position at which it couples on colour-development an acid grouping selected from carboxylic and sulphonic acid groups and yielding on colour-development a 9 record dye image which absorbs undesirably to some extent light of wavelengths which it is desired that it should transmit, subjecting the said photographic material to colour-development to form dye record images in yellow, magenta and cyan and treating the resulting material with a basic dyestuff, thereby forming with the residual acid colour-former an image of opposite sign to the record dye image from such acid colour-former in a complex of residual acid colour-former and said basic dye and reducing the density of the complementary image thus obtained by controlled treatment with a colourless cation-active compound, the hue and final intensity of such image of opposite sign being such that it absorbs light of at least some of the wavelengths which the record dye image in the said layer containing the said acid colour-former undesirably absorbs, so that the absorption of such wavelengths is substantially uniform over RONALD BERNARD COLLINS. DOUGLAS JAMES FRY. OLIVER EDMUND PRATT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,306,410 Schinzel Dec. 29, 1942 2,441,491 Kendall et a1 May 11, 1948 OTHER REFERENCES Journal of the American Chemical Society, volume 71, July 1949, pages 2287-2290. 

